The study is based on experimental results for the seismic response of a pre-cast single storey RC industrial frame and cyclic tests of pre-cast columns. The experimental data for the industrial frame have shown that under seismic excitations the curvatures below the top of the foundation exceed those above it. This fact cannot be explained only by the tensile strain penetration phenomenon. The records of the relative displacements at the bottom of the instrumented columns are used to estimate the contact forces acting on the faces of the columns connected to the pocket. The calculated contact forces differ significantly from their classic presentation as friction force when pressing force to the respective interface is applied. The presence of considerable contact forces at the tensed side of the columns is proved. This phenomenon is explained by the flexural deformation of the column surface, which applies pressure to the plane surface of the grout in their interaction. For small negative strains the surfaces of the column and the grout are coupled by a considerable contact force, which is linearly proportional to the strain and depends on the magnitude of the affected by the axial force initial deformation. Based on the considered experimental results, the upper boundary of the initial compression strains when considerable curvatures below the top of the foundation occur is set up. A refined model of the column-foundation connection, which agrees well with the experimentally assessed behaviour is presented. It makes possible to introduce a simplified expression for the pressing force on the pocket faces, needed for the assessment of the horizontal reinforcement around the top half of the pocket. The expression gives well coinciding with the experimental data and slightly conservative results for the maximum value of the pressing force and could be easily implemented in the design practice.